How many of you run synthetic 5w40 all year round even in hi temp summer months during heavy towing? My duramax owners manual state not to run 5w40 oils in 90 plus degree temps...I know that GM is concerned about shearing, but I have seen excellent used oil analysis on this website with people running 10w30 HDEO's in summer..I know that all "synthetic" oils are not the same as far as group type..but im my mind any "synthetic" 5w40 should be better than a conventional 15w40 hdeo? What gives?? I should add that my duramax is modified with a computer tuner..which obviously stresses oil more than factory settings, I want to run Delvac 5w40 ESP year round here in michigan which is a group 4 oil...should i stick with delvac 15w40 in summer and delvac 5w40 only in winter??
Question for duramax owners..
- Thread starter Ponch
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Ponch, use syn at any temp. I have mobil delvac 5w40 in mine from dealer.
people in socal are using amsoil syn diesel oil, temps there were 99F last week in Nov. once my free syn changes at dealer runs out, I will switch to 10w30 (menards) rotella for winters,
people in socal are using amsoil syn diesel oil, temps there were 99F last week in Nov. once my free syn changes at dealer runs out, I will switch to 10w30 (menards) rotella for winters,
dnewton3
Staff member
I don't really know why GM/Isuzu tends to shy from 5w-40. Perhaps it's the concern over that makes the 5w-40 tick (a group III with a lot of VII's versus group IV?).
Fankly, I couldn't care less. There are far too many used oil analysis out there to show that most any grade/brand will perform well in a Dmax. The Dmax is simply very easy on oil, period. And the wear results from all those used oil analysis show that the Dmax is not sensitive to the typd/brand/grade of HDEO used. ( I will throw in a caveot here, in that some brands of PAOs tend to make the engine shed Cu excessivly; generally accepted to be a cooler issue and not detrimental to the engine, although it certainly skews the used oil analysis).
Most people know that I'm a staunch dino HDEO user, but I respect syn's greatly, when people use them appropriately. But for any given perceived "advantage" of a base stock upgrade, there are also viscosity changes that can attain similar, if not the same, results.
Case in point:
* I once ran Rotella T Synthetic 5w40 (CI-4) in my Dmax; ran fine; used oil analysis good.
* I've since run Delvac 1300 (a used oil analysis sample is on my shelf in the garage, but I cannot find the sense of sending it in when I've seen scores of others confirming the Delvac/Dmax combo to be outstanding).
* I'd run Tection Extra a few year ago; no issues; used oil analysis fine.
* I am back on 10w30 Rotella dino now. My last load of conventional 10w30 Rotella resulted in an fantatic used oil analysis even after hard, heavy, hot towing, and cold starts below zero in winter.
* And, as you know, there are PAO 5w30 HDEOs on the market from Amsoil and Castrol, among others. I've seen good used oil analysis from them as well.
In a Dmax, it just does not matter what you run. If you spend a significant amount of time below zero deg F, then I would suggest either a 5w-40 of 10w30. Don't sweat the details here when all the evidence shows it simply does not matter.
Fankly, I couldn't care less. There are far too many used oil analysis out there to show that most any grade/brand will perform well in a Dmax. The Dmax is simply very easy on oil, period. And the wear results from all those used oil analysis show that the Dmax is not sensitive to the typd/brand/grade of HDEO used. ( I will throw in a caveot here, in that some brands of PAOs tend to make the engine shed Cu excessivly; generally accepted to be a cooler issue and not detrimental to the engine, although it certainly skews the used oil analysis).
Most people know that I'm a staunch dino HDEO user, but I respect syn's greatly, when people use them appropriately. But for any given perceived "advantage" of a base stock upgrade, there are also viscosity changes that can attain similar, if not the same, results.
Case in point:
* I once ran Rotella T Synthetic 5w40 (CI-4) in my Dmax; ran fine; used oil analysis good.
* I've since run Delvac 1300 (a used oil analysis sample is on my shelf in the garage, but I cannot find the sense of sending it in when I've seen scores of others confirming the Delvac/Dmax combo to be outstanding).
* I'd run Tection Extra a few year ago; no issues; used oil analysis fine.
* I am back on 10w30 Rotella dino now. My last load of conventional 10w30 Rotella resulted in an fantatic used oil analysis even after hard, heavy, hot towing, and cold starts below zero in winter.
* And, as you know, there are PAO 5w30 HDEOs on the market from Amsoil and Castrol, among others. I've seen good used oil analysis from them as well.
In a Dmax, it just does not matter what you run. If you spend a significant amount of time below zero deg F, then I would suggest either a 5w-40 of 10w30. Don't sweat the details here when all the evidence shows it simply does not matter.
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we run 15w40 Amsoil year round. The D'max is simply not hard on oil at all.
I've ran AMSOIL 15w40 for the past 3 ocis but this time im switching to rotella t6 because when it gets real cold I don't like seeing the pressure gauge maxed out at 120psi.
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dnewton3
Staff member
I don't think you can fairly say "real cold" and Virginia Beach go together ...
people complain about the cold at 50 degrees here!
dnewton3
Staff member
Yes, SteveSRT8, you are correct; everything is viewed from a "perspective".
But "reall cold" to an HDEO lube means a bit cooler than the average low of 32 deg F in January in Virginia Beach, VA.
But "reall cold" to an HDEO lube means a bit cooler than the average low of 32 deg F in January in Virginia Beach, VA.
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The minimum allowed HTHS viscosity (150°C) is 3.5 mPa for 5W-40 and 3.7 for 15w40. Could that be the reason GM doesn't recommend 5W-40 in those engines? Some diesel rated 5W-40 oils easily exceed that, and some might just meet the minimum.
Try asking the oil company of your preference if they recommend their 5W-40 in a Duramax.
Try asking the oil company of your preference if they recommend their 5W-40 in a Duramax.
RTS in ours no issues....
I've been running the Shell Rotella T5 10w30 for a while now, Duramax runs just fine. I will switch to Amsoil ACD 10w30 diesel synthetic next oil change to use the oil for more mileage. I've always ran 10w30 grade in my LBZ Duramax, its the only grade I run year round.
I've thought about switching to the Shell T5 10w30 oil in my 07 LBZ Duramax. I've been running Shell Rotella 15w40. Would there be any noticeable MPG increase if I change to 10w30? I occasionally tow a 13K LB 5th wheel camper about 4-5 times a year. I also run B100 biodiesel most always except during the colder months in which I have to blend my fuel.
dnewton3
Staff member
I have not seen a significant savings with the lower vis grade, nor did Arkapigdiesel when he tried it.
I suspect it's just a large vs small picture things. We probably can't quantify the savings for most of us, but the OEMs can show statistical savings in their CAFE ratings.
I use it because I get a bit better winter starts and still have great summer wear protection. If I save any money in fuel, I can't tell it. OTOH, it certainly cannot be costing me money to use oil of a lighter grade. No downside, with a potential upside.
I suspect it's just a large vs small picture things. We probably can't quantify the savings for most of us, but the OEMs can show statistical savings in their CAFE ratings.
I use it because I get a bit better winter starts and still have great summer wear protection. If I save any money in fuel, I can't tell it. OTOH, it certainly cannot be costing me money to use oil of a lighter grade. No downside, with a potential upside.
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